Wafer processing in a chamber with novel gas inlets

ABSTRACT

A system for supplying processing fluid to a substrate processing apparatus having walls, the inner surfaces of which define a processing chamber in which a substrate supporting susceptor is located. The system consists of a number of fluid storages, each which stores a separate processing fluid, at least two fluid conduits along which processing fluid flows from the fluid storages to the processing apparatus and a fluid inlet which connects the fluid conduits to the processing chamber. The inlet has a separate fluid passage, corresponding to each of the fluid conduits, formed along it. Each fluid passage opens at or near an inner surface of a wall to together define a fluid mixing zone, so that fluid moving along one fluid passage is prevented from mixing with fluid moving along any other passage until reaching the mixing zone.

RELATED CASES

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 08/099,977 filed on Jul. 30, 1995 in the name of Anderson, etal.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to semiconductor processing apparatus and,more particularly, to a method and apparatus of supplying two differentprocessing gases to a semiconductor wafer processing chamber.

[0004] 2. Brief Description of the Prior Art

[0005] Present-day equipment for the semiconductor industry is movingtoward single substrate processing because processing chambers can bemade smaller and processing can be better controlled. Further, modernsemiconductor vacuum processing systems have been developed to carry outmore than one processing step on a substrate without removing thesubstrate from a vacuum environment. The use of such vacuum systemsresults in a reduced number of particulates that contaminate the surfaceof the wafer during processing, thereby improving the device yield.

[0006] A typical example of a modern CVD processing apparatus is shownin FIG. 1. In this figure, a single substrate reactor 10 is shown toinclude a top 12, side walls 14 and a lower portion 16 that, together,define a chamber 18 into which a single substrate, such as a siliconwafer 20, can be loaded. The wafer 20 is mounted on a susceptor 22 thatcan be rotated by a drive 23 to provide a time-averaged environment forthe wafer 20 that is cylindrically symmetric.

[0007] A preheat ring 24 is supported in the chamber 18 and surroundsthe susceptor 22. The wafer 20 and the preheat ring 24 are heated bylight from a plurality of high-intensity lamps, schematically indicatedas 26, mounted inside of the reactor 10. The top 12 and lower portion 16of the reactor 10 are typically made from clear quartz which istransparent to the light from lamps 26. Quartz is generally used to makeup the top 12 and lower portion 16 because it is transparent to light ofboth visible and IR frequencies, because it exhibits a relatively highstructural strength and because it is chemically stable in the processenvironment of the chamber.

[0008] During the deposition process, processing gas (whether reactantor dopant) is supplied to the interior of the chamber 18 from anexterior source, schematically represented by two tanks 28. The gasflows from the gas supply 28 along a gas supply line 30 and into thechamber 18 via a gas inlet port 32. From the port 32, the gas flowsacross the preheat ring 24 where it heats up, across the susceptor 22and wafer 20 in the direction of the arrows 34, to be evacuated from thechamber 18 through evacuation port 36. The dominant shape of the flowprofile of the gases is laminar from the gas input port 32 and acrossthe preheat ring 24 and the wafer 20 to the exhaust port 36, even thoughthe rotation of the wafer 20 and thermal gradients caused by the heatfrom the lamps 26 do affect the flow profile slightly.

[0009] The above-described CVD processing chamber can accommodate anumber of different processes taking place. Each process differs,depending on the desired end result, and has different considerationsassociated therewith.

[0010] In the polysilicon deposition process, doped or undoped siliconlayers are typically deposited onto the wafer using processes such aslow-pressure chemical vapor deposition (CVD). In this process, areactant gas mixture including a source of silicon (such as silane,disilane, dichlorosilane, trichlorosilane or silicon tetrachloride) and,optionally, a dopant gas (such as phosphine, arsine or diborane) isheated and passed over the wafer to deposit a silicon film on itssurface. In some instances, a non-reactant carrier gas, such ashydrogen, is also injected into the processing chamber, together witheither or both of the reactant or dopant gases. In this process, thecrystallographic nature of the deposited silicon depends upon thetemperature of deposition. At low reaction temperatures, the depositedsilicon is mostly amorphous; when higher deposition temperatures areemployed, a mixture of amorphous silicon and polysilicon or polysiliconalone will be deposited.

[0011] One problem with the doped polysilicon deposition is that thetemperature dependence of dopant incorporation is the opposite of thetemperature dependence of the polysilicon deposition rate. This isbecause adjusting the temperature to obtain thickness uniformity in thepolysilicon layer produces a non-uniform dopant incorporation. This isbecause the dopant gas has, in the past, been incorporated into theprocessing gas before it is injected into the chamber. There istherefore no control of the dopant gas flow independent of the flow ofthe silicon species processing gas.

[0012] In another process, the nitride deposition process, a stream ofreactant gas, which is a mixture of ammonia (NH₃) and any one of thevarious silane species, is injected into the chamber. These two gasesreact at room temperature to produce small crystals. In the arrangementshown in FIG. 1, the gas storage 28 is shown to include two tanks, bothof which feed into a single supply line 30. If these tanks containedammonia and silane respectively and the line 30 were at roomtemperature, this reaction would occur and particles would form alongthe entire length of the supply line 30 and within the manifold 32.These particles are undesirable, as they are a source of contaminationin the chamber 18; and their existence should therefore be eliminated.

[0013] In addition, it has been found that some reactant gases passthrough the gap between the preheat ring 24 and the susceptor 22. Thiscauses deposition on the back side of the susceptor 22 and on some ofthe other components in the lower portion of the chamber 18. Suchdeposition is both wasteful and undesirable, as it requires additionalcleaning to remove.

[0014] Accordingly, a need has arisen for a system of supplyingreactant/dopant gases to a semiconductor processing chamber whichovercomes these different problems.

SUMMARY OF THE INVENTION

[0015] Summary

[0016] Briefly, this invention provides for a system for supplyingprocessing fluid to a substrate processing apparatus having walls, theinner surfaces of which define a processing chamber in which a substratesupporting susceptor is located. The system consists of a number offluid storages, each which stores a separate processing fluid, at leasttwo fluid conduits along which processing fluid flows from the fluidstorages to the processing apparatus and a fluid inlet which connectsthe fluid conduits to the processing chamber. The inlet has a separatefluid passage, corresponding to each of the fluid conduits, formed alongit. Each fluid passage opens at or near an inner surface of a wall totogether define a fluid mixing zone, so that fluid moving along onefluid passage is prevented from mixing with fluid moving along any otherpassage until reaching the mixing zone.

[0017] Typically, at least two of the fluid passages are verticallydisplaced from one another to, at least partially, define upper andlower fluid flow paths. The fluid inlet may include a mixing cavityformed at or near the inner surface of the wall so that the mixing zoneis defined by the boundaries of the mixing cavity. The mixing cavity maybe a generally vertical channel disposed between the upper and lowerfluid flow paths.

[0018] Alternatively, the chamber can be divided into an upper and alower portion by the susceptor and the upper and lower fluid flow pathsarranged respectively to open into the upper and lower portions of thechamber. In this arrangement, the chamber typically includes asusceptor-circumscribing preheat ring which defines an annulus betweenit and the susceptor. The lower fluid flow path would include theannulus; and, in operation, processing fluid passing into the lowerportion of the chamber will pass through this annulus to mix withprocessing fluid in the upper portion of the chamber.

[0019] The details and advantages of the present invention will, nodoubt, become apparent to those skilled in the art after having read thefollowing detailed description of the preferred embodiments which areillustrated in the several figures of the drawing.

IN THE DRAWING

[0020] In the accompanying drawing:

[0021]FIG. 1 is a cross section of a prior art CVD semiconductor waferprocessing chamber;

[0022]FIG. 2 is a cross section through the gas inlet manifold of oneembodiment of the invention;

[0023]FIG. 3 is a plan view of a portion of a CVD processing chamberillustrating some of the components of the manifold of FIG. 2;

[0024]FIG. 4 is a pictorial exploded view showing some of the componentsof the manifold of FIG. 2;

[0025] FIGS. 5(a) to 5(e) are cross sections of alternative embodimentsto the manifold illustrated in FIG. 2;

[0026]FIG. 6 is a figure similar to that in FIG. 1, but showingschematically how gases can be supplied to the chamber to reduce backside wafer deposition;

[0027]FIG. 7 is a plan view similar to that in FIG. 3, showing how themanifold can be divided to make allowance for different types of gassupply; and

[0028]FIG. 8 is a schematic flow diagram showing how different mixturesof gases can be regulated and supplied to an epitaxial depositionchamber.

DESCRIPTION OF THE EMBODIMENTS

[0029] Referring jointly to FIGS. 2, 3 and 4, the improved gas inletmanifold, generally indicated as 100 of the invention, can be seen. Themanifold 100 is shown in FIGS. 2 and 3 as connected to the side wall 14(constituted by upper and lower clamp rings 40, 42 and a base ring 44)of a semiconductor processing apparatus 18

[0030] In all three of these figures, the manifold 100 is shown toinclude a connector cap 102, a diffuser plate 104 and an interface 106.The connector 102 and the interface 106 have upper and lower fluidpassages 108, 110 formed therein. As is apparent from FIG. 4, theseupper and lower fluid passageways are oblate in cross section. Thediffuser plate 104, on the other hand, has an upper and a lower row ofcircular holes 112 formed therein. When the plate 104 is in positionbetween the cap 102 and the interface 106, the upper and lower rows ofholes 112 correspond respectively to the upper and lower fluid passages108, 110. The function of these holes will be described further below.

[0031] The connector cap 102 is connected to a plurality of upper andlower gas conduits 114, 116. These conduits 114, 116 are, in turn, partof gas supply system (not shown) and serve to transport processing gasesfrom a gas supply to the chamber 18. Along the inside wall of thechamber 18, a circular quartz ring 119 is disposed. In the vicinity ofthe manifold 100, the quartz ring has upper gas and lower gaspassageways 120, 122 formed therein. These upper and lower gaspassageways 120, 122 are aligned and communicate directly with the gaspassageways 108, 110 formed in the interface 106. In the body of thequartz ring, the lower gas passageway 122 is connected to the upper gaspassageway 120 by means of a vertically disposed slot 124 which, whenviewed in plan, defines an arc.

[0032] In operation, processing gas is supplied to the manifold 100 bymeans of conduits 114, 116. These gases are kept separate and flowrespectively along upper and lower conduits 108, 110. As the gases aresupplied from individual gas pipes 114, 116 to the upper and lowerconduits 108, 110, individual streams of gases, each relating to one ofthe conduits 114,116, occur in the connector cap 102.

[0033] These gases bank up against the upstream side of the diffuserplate 104 and pass through the holes 112 formed therein. As a result ofthe diffuser plate, the gas streams respectively found in the upper andlower conduits 108, 110 are broken down and form a substantially laminarflow of gas in the interface 106. When the gas in the lower conduit 110reaches the quartz ring 118, it moves along the lower gas path 122 andup the vertically disposed slot 124 to meet and mix with the gas in theupper conduit 108. At this point, the gas has been heated to some extentby the quartz ring 118 which, in turn, has been heated by the lamps. Asa result of this arrangement, the gas is preheated before mixing occurs;and undesirable crystals do not form. This mixture of gas is then ableto move in a substantially laminar pattern across the preheat ring 24,the susceptor 22 and the wafer 20, to be exhausted through the exhaust36.

[0034] As can be seen from FIGS. 3 and 4, the interface 106 has a flatupstream face 130 and a curved downstream face 132. This allows theinterface 106 to provide a gas flow path between the flat-facedconnector cap 102 and diffuser plate 104, on the one hand, and thecircular quartz ring 119, on the other hand. In addition, FIGS. 2 and 4show that the diffuser plate 104 fits into a recess 134 formed in theconnector cap 102. As a result of this configuration, the interface 106,which is typically made of quartz, abuts against both the diffuser plate104 and the connector cap 102.

[0035] In FIGS. 5a-5 e, different configurations of channels, generallyindicated as 140, are shown formed in the quartz ring 119. Thesechannels 140 all serve approximately the same function as the channels120, 122 shown in FIG. 2, and these figures serve to illustrate a numberof different configurations of channels that can be used to allow themixing of the gases to occur as close as possible to the interior faceof the quartz ring 118. Apart from the different configurations of thechannels 140, all the other components shown in FIGS.5a-5 e identical toor similar to corresponding components illustrated in FIGS. 2 through 4.Accordingly, they have been given like reference numerals.

[0036] The embodiments illustrated in these FIGS. 2 to 5 thereforeprovide a solution to the problem of gases reacting spontaneously in thesupply conduits and inlet manifold in the nitride deposition processdescribed above. It will be understood that the principles illustratedin these figures could be applied to processes other than the nitridedeposition process.

[0037] A different embodiment of the invention is illustrated in FIG. 6.This figure shows a typical CVD deposition chamber generally indicatedas 210. As with the prior art deposition chamber 10 indicated in FIG. 1,the apparatus includes a top 12, side walls 14 and lower portion 16,which together define a processing chamber 218. Inside the chamber 218,a semiconductor wafer 20 is supported on a susceptor 22. A susceptorcircumscribing preheat ring 24 is also shown. Processing gases are inputfrom different sources (not shown) into the chamber 218 by way of inputmanifold 232 and are exhausted from the chamber by means of exhaust port36. For clarity, the heater lamps and other components of the apparatusare not illustrated.

[0038] As is apparent from this figure, the preheat ring 24 and thesusceptor 22 divide the chamber 218 into an upper and lower zone 218 aand 218 b, respectively.

[0039] This embodiment of the invention can also be used to combat theundesirable reaction between ammonia and silicon species gases in thenitride deposition process. This can be done by injecting each gas froma different source separately into one of the upper or lower portions ofthe chamber 218 respectively through upper and lower passageways 232 aand 232 b. This means that the gases do not mix until they are fullyinside the chamber 218.

[0040] For example, the silicon species gas can be injected into theupper zone 218 a whilst the ammonia based gas can be input into thelower zone 218 b. If the ammonia input into the lower zone 218 b is at aslightly higher pressure than the silicon species gas input into theupper zone 218 a, the ammonia gas will flow (in the direction indicatedby arrows 222) from the lower zone to the upper zone by way of the slitbetween the preheat ring 24 and the susceptor 22 in the direction of thearrows 220. Thus, both the ammonia gas and the silicon gas are heatedwithin the chamber before they come into contact with one another.Furthermore, mixing of the gases occurs at or close to the wafer, andunwanted particle formation is reduced.

[0041] This configuration also has the advantage that the gas movingthrough the slit between the preheat ring 24 and the susceptor 22prevents gases from moving from the upper zone 218 a to the lower zone218 b. This restricts the amount of deposition that occurs on the backside of the susceptor 22 and the other components within the lower zone218 b of the processing apparatus 210. It is important to restrictdeposition on the back side of the susceptor, as it may adversely affecttemperature measurements (usually done by means of an externalpyrometer) which, in turn, will adversely affect processing of the wafer20. Deposition on the other components in the lower zone 218 b isundesirable, as it could lead to particle generation if not removed. Inaddition, wafer transfer occurs in this lower zone 218 b and substantialparticle generation could adversely affect the moving parts in thiszone.

[0042] This embodiment of the invention also has the advantage that itcan be used to reduce the problem (as described above) associated withdoped polysilicon deposition. As will be recalled, the temperaturedependence of dopant incorporation is opposite to the temperaturedependence of the polysilicon deposition rate. This embodiment providesthe flexibility of inputting the dopant gas into the lower zone 218 band being able to independently control its flow. Therefore, anadditional and independent source of control over dopant incorporationcan be achieved.

[0043] The embodiment of FIG. 6 can be used in conjunction with afurther system of improving the control of different types of gasesflowing into the processing chamber as illustrated in FIGS. 7 and 8.These figures show only the interfacing connector 306, portions of theprocessing apparatus, the wafer 20, susceptor 22, preheat ring 24 andgas outlet port 36. FIG. 7 shows only the portion of the gas inletmanifold 332 which supplies the gas to the upper zone of the processingchamber, and FIG. 8 schematically represents a gas control system.

[0044] The interfacing connector 306 is shown to be constituted by acentral zone 308 and an outside zone 310. According to this embodimentof the invention and as further illustrated in FIG. 8, the compositionof the gas which flows into the central zone 308 can be controlledindependently of the composition of the gas which flows into the outsidezones 310. In addition, the flow rate of the gas to either of the twohalves 308 a, 308 b of the central zone can further be controlledindependently from one another. This provides two degrees of control forthe gas flow system for the purpose of controlling the composition ofany layer deposited on the semiconductor wafer 20. In addition, thechamber heating system provides the third control variable (i.e.,temperature). As in the past, the susceptor 22 can be rotated to improvethe uniformity of the deposition on the wafer 20.

[0045] Turning now to the diagram in FIG. 8, it can be seen that a gascontaining silicon, together with a hydrogen carrier gas, is fed to thechamber 318 from containers 302, 304 by means of independent mass flowcontrollers 303, 305. This gas mixture flows through two bellowsmetering valves 311, 312 which operate as variable restricters andapportion the main flow of silicon bearing gas between the center andouter zones 308, 310, respectively. In addition, a gas which is a dopantsource (such as diborane diluted in hydrogen) is fed from storage 314into two different mass flow controllers 316, 320 and then metered intothe silicon source downstream of the bellowing metering valves 311, 312.

[0046] As a result of this configuration, separate control of the dopantgas concentration flowing into the central zone and the outer zone 308,310, respectively, can be achieved.

[0047] Although the present invention has been described above in termsof specific embodiments, it is anticipated that alterations andmodifications thereof will no doubt become apparent to those skilled inthe art. It is therefore intended that the following claims beinterpreted as covering all such alterations and modifications as fallwithin the true spirit and scope of the invention.

What is claimed is:
 1. A fluid supply system for supplying a processingfluid to a walled substrate processing chamber, the system comprising:(a) a first fluid inlet for directing a first fluid flow into thechamber through a first chamber wall; and (b) a second fluid inlet,separated from the first fluid inlet, for directing a second fluid flowinto the chamber, the first and second inlets being configured to causethe first and second fluids to mix at a fluid mixing zone at an innersurface of the first chamber wall and be directed, toward a substratesupported within the chamber, in a mixed fluid path approximately aswide as the substrate's major dimension taken transverse the mixed fluidpath.
 2. The system as recited in claim 1, wherein the fluid inlets areconfigured to cause the mixed fluid flow path to be generally parallelto a processing surface of the substrate.
 3. The system as recited inclaim 2, wherein the first and second conduits are configured to givetheir respective fluid flows a planar characteristic.
 4. The system asrecited in claim 3, wherein the first and second conduits are configuredto cause the first fluid flow to intersect the second fluid flow at themixing zone.